1. Field of the Invention
This invention relates to apparatus having power supply circuitry that employs an energy storage element to provide holdover power to a load. This invention further relates to power supply circuitry that employs a high-density low voltage energy storage device to provide holdover power to a load.
2. Statement of the Problem
In modern power system design for equipment such as computer servers or telecommunications network elements, a need exists for a certain amount of holdover energy storage on each field or replicable unit. This holdover energy storage is often referred to as “hold up capacitance” and permits the field or replicable unit to maintain normal operation even if there is a momentary interruption of its primary power source. Such interruptions are common when a fault in a particular unit causes its power fuse to blow. All other units connected to the same power source then experience a severe momentary voltage dip or transient. This can occur during rectifier switchovers, reconfiguration of universal power supplies, and power feeder reconfigurations. For high power units, the capacitance needed to store the required holdover energy can be large, physically big and expensive. A need therefore exists for apparatus that reduces the size and cost impact of the required holdover energy source while still providing the required holdover energy protection.
A capacitor is the simplest and least expensive apparatus for providing holdover power. The magnitude of the capacitance and the magnitude of the load to which the capacitor is connected define the duration of the holdover time. The holdover time provided by low-density capacitors of a readily obtainable capacitance and physical size is in the order of microseconds. Longer holdover times are obtainable when larger capacitors are used. However, the duration of the obtainable holdover times is often limited by the space available to house the larger capacitors, and their affordability.
It is known to use backup batteries to provide holdover power. But, batteries can be expensive and may require the use of banks of batteries having a capacity sufficient to power a load for minutes or hours when interruption of commercial power occurs. Power supplies having this holdover power capability are not economically feasible for many applications. The cost, weight, and size of such power supplies exceed the available space and cost of the circuitry to be protected.
Electronic circuitry of the type used in computer servers and communication equipment is often modular or space limited and has a need for protection against power transients in the order of milliseconds. To be economically feasible, the holdover power apparatus should be proximate to the load to be protected. Also, it should be small in size and not occupy an inordinate amount of space on the circuit board or module containing the load circuitry to be protected.
It is therefore a problem to equip electronic circuitry with holdover power protection that is economical in size and cost.